By default, the fields that you add to the Value panel will be displayed in the column names of the Groups Table with the name of the function that was used to create the field. Edit the query to give names to the fields.

Consider the following example for the query that is currently used to run link feature:

'Log Source' = 'EBS Concurrent Request Logs - Enhanced'
| link 'Request ID'
| stats earliest('Event Start Time') as 'Request Start Time', 
latest('Event End Time') as 'Request End Time',
unique(Application),
unique('Program Details')  
| eval 'Time Taken' = 'Request End Time' - 'Request Start Time'
| classify topcount = 300 'Request Start Time', 'Time Taken' as 'Request Analysis'

To change the names of the fields unique(Application) to Application Name and unique('Program Details') to Job, modify the query:

'Log Source' = 'EBS Concurrent Request Logs - Enhanced'
| link 'Request ID'
| stats earliest('Event Start Time') as 'Request Start Time', 
latest('Event End Time') as 'Request End Time',
unique(Application) as 'Application Name',
unique('Program Details') as Job  
| eval 'Time Taken' = 'Request End Time' - 'Request Start Time'
| classify topcount = 300 'Request Start Time', 'Time Taken' as 'Request Analysis'

After renaming the fields, you can refer to the fields using the new names. The column names in the Groups Table will have the new names of the fields.